Effects of pH and low molecular weight organic acids on competitive adsorption and desorption of cadmium and lead in paddy soils

The bioavailability and ultimate fate of heavy metals in the environment are controlled by adsorption-desorption process. Batch equilibrium experiments were performed to assess the effects of pH and low molecular weight organic acids (LMWOAs) on competitive adsorption and desorption of cadmium and lead in paddy soils from China. The results indicated that both soils exhibited greater sorption capacity for lead (Pb) (1.37-1.61-fold) than cadmium (Cd) as estimated by the maximum sorption parameter (Q) from the Langmuir equation. The Langmuir bonding energy coefficient (b) and distribution coefficient (K (d)) were greater for Pb than for Cd, furthermore, b (binary) and K (d) (single) were greater than b (single) and K (d binary), indicating that competition for sorption sites promote the retention of both metals on more specific sorption sites. Both Cd and Pb desorption as a function of solution pH was characteristic of "S" pattern. The presence of LMWOAs inhibited Cd or Pb desorption at the low concentrations (≤0.1 mmol L(-1)) but promoted Cd and Pb desorption at higher concentrations (≥0.5 mmol L(-1) for citric acid and ≥1 mmol L(-1) for malic and oxalic acid). The two paddy soils had a greater d (Cd) than d (Pb) in the presence of LMWOAs, indicating that Cd desorption was more affected by the presence of LMWOAs in binary metal system.     

Effect of citric acid on metals mobility in pruning wastes and biosolids compost and metals uptake in <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>

To assess metal mobility in pruning waste and biosolids compost (pH?6.9 and total concentration of metals in milligram per kilogram of Cd 1.9, Cu 132, Fe 8,513, Mn 192, Pb 81, and Zn 313), shrubs species Atriplex halimus and Rosmarinus officinalis were transplanted in this substrate and irrigated with citric acid (4 g?L^?1, pH?2.9) and nutrient solution daily for 60 days. Citric acid significantly increased the concentrations of soluble Mn and Fe in the nutrient substrate solution measured by suction probes, while other metals did not vary in concentration (Cu and Zn) or were not observed at detectable levels (Cd and Pb). In plants, citric acid significantly increased the concentrations of Cu (2.7?±?0.1–3.3?±?0.1 mg?kg^?1), Fe (49.2?±?5.2–76.8?±?6.8 mg?kg^?1), and Mn (7.2?±?1.1–11.4?±?0.7 mg?kg^?1) in leaves of R. officinalis, whereas the concentration of only Mn (25.4?±?0.3–42.2?±?2.9 mg?kg^?1) was increased in A. halimus. Increasing Fe and Mn solubility by citric acid addition indicates the possibility of using it to improve plant nutrition. The mobility of metals in this substrate was influenced for the concentration of the metal, the degree of humification of organic matter and its high Fe content.     

Metal release from serpentine soils in Sri Lanka

Ultramafic rocks and their related soils (i.e., serpentine soils) are non-anthropogenic sources of metal contamination. Elevated concentrations of metals released from these soils into the surrounding areas and groundwater have ecological-, agricultural-, and human health-related consequences. Here we report the geochemistry of four different serpentine soil localities in Sri Lanka by coupling interpretations garnered from physicochemical properties and chemical extractions. Both Ni and Mn demonstrate appreciable release in water from the Ussangoda soils compared to the other three localities, with Ni and Mn metal release increasing with increasing ionic strengths at all sites. Sequential extraction experiments, utilized to identify “elemental pools,” indicate that Mn is mainly associated with oxides/(oxy)hydroxides, whereas Ni and Cr are bound in silicates and spinels. Nickel was the most bioavailable metal compared to Mn and Cr in all four soils, with the highest value observed in the Ussangoda soil at 168?±?6.40 mg kg^?1 via the 0.01-M CaCl₂ extraction. Although Mn is dominantly bound in oxides/(oxy)hydroxides, Mn is widely dispersed with concentrations reaching as high as 391 mg kg^?1 (Yudhaganawa) in the organic fraction and 49 mg kg^?1 (Ussangoda) in the exchangeable fraction. Despite Cr being primarily retained in the residual fraction, the second largest pool of Cr was in the organic matter fraction (693 mg kg^?1 in the Yudhaganawa soil). Overall, our results support that serpentine soils in Sri Lanka offer a highly labile source of metals to the critical zone.     

Fractionation of Aluminum in Soil and Relation to Its Concentration in Fruits

Aluminum concentrations in the fruit samples taken from different regions were determined by atomic absorption spectrometry after dry ashing digestion. To identify the aluminum phases being most responsible for fruit-available aluminum, the soil samples near the fruit plants were also analyzed for aluminum by using various digestion and selective extraction reagents. The relation between the aluminum concentrations in fruits and in soil extracts was studied. The obtained aluminum concentrations in the fruits were in the range of 1.5 to 42.0 mg kg^-1 on dry weight basis. It was observed that the aluminum concentrations of morello cherry(R² = 0.79) and mulberry (R² = 0.99) were correlated to the aluminum concentrations in citric acid extracts of the soils. While the aluminum concentrations of the EDTA and acetic acid extracts in some soils samples include 35% and 25% of total aluminum, respectively, the other soils contain only 1–2%.     

棕壤吸附-解吸铬影响因素研究

采用室内实验方法,研究了不同铬浓度及不同pH对棕壤吸附-解吸铬的影响,草酸、EDTA和柠檬酸3种有机酸在不同浓度、不同pH条件下对棕壤吸附-解吸铬的影响。结果表明,棕壤对Cr6＋的吸附率随其浓度的增大逐渐增大,并在酸性条件下易于吸附Cr6＋,在碱性条件下易于解吸Cr6＋,低浓度有机酸有利于棕壤对Cr6＋的解吸。EDTA解吸率最大,草酸次之,柠檬酸最小。     

Measurement of total antimony and antimony species in mine contaminated soils by ICPMS and HPLC-ICPMS

This paper describes the measurement of total antimony and antimony species in "real world" mine contaminated sediments using ICPMS and HPLC-ICPMS. Low and high temperature microwave extraction procedures (90 degrees C and 150 degrees C, respectively) using a range of nitric-hydrochloric acid combinations were examined as to their efficacy to extract antimony from six mine contaminated soils and a certified reference material. The use of the higher temperature with nitric-hydrochloric acid (1:2 (v/v)) was suitable to release antimony from sediments and the certified reference material, NIST 2710 Montana soil. Antimony concentrations obtained using this acid mixture were similar to those obtained using a more aggressive extraction with nitric, hydrochloric, perchloric and hydrofluoric acid mixture. A 25 mM citric acid solution at 90 degrees C for 15 min extracted 47-78% of antimony from soils. A Hamilton PRP X-100 anion exchange column with 20 mM EDTA mobile phase, pH 4.5, flow rate 1.5 mL min(-1) and column temperature of 50 degrees C was used to separate antimony species. Column recoveries ranged from 78-104%. The predominant form of antimony was Sb(5+). Little conversion of Sb(5+) occurred (<5%) during extraction, however, significant conversion of Sb(3+) occurred (approximately 36%). The extraction of antimony species with citric acid should be useful in the determination of inorganic antimony available to plants, as plants commonly excrete carboxylic acids, including citric acid, into their rhizospheres to mobilise trace elements for nutritional purposes.     

Effects of pig manure containing copper and zinc on microbial community assessed via phospholipids in soils

Pig manure (PM) is widely used as an organic fertilizer to increase yields of crops. Excessive application of compost containing relatively great concentrations of copper (Cu) and zinc (Zn) can change soil quality. To clarify the effects of different rates of application and to determine the optimal rate of fertilization, PM containing 1,115 mg Cu kg^?1, dry mass (dm) and 1,497 mg Zn kg^?1, dm was applied to alkaline soil at rates of 0, 11, 22, 44, 88, and 222 g PM kg^?1, dm. Phospholipid fatty acids (PLFAs) were used to assess soil microbial community composition. Application of PM resulted in greater concentrations of total nitrogen (TN), NH₄ ⁺-N, NO₃ ^?-N, total carbon (TC), soil organic matter (SOM) but lesser pH values. Soils with application rates of 88–222 g PM kg^?1, dm had concentrations of total and EDTA-extractable Cu and Zn significantly greater than those in soil without PM, and concentrations of T-Cu and T-Zn in these amended soils exceeded maximum limits set by standards in china. Except in the soil with a rate of 11 g PM kg^?1, dm, total bacterial and fungal PLFAs were directly proportional to rate of application of PM. Biomasses of bacteria and fungi were significantly greater in soils with application rates of 44–222 g PM kg^?1, dm than in the soil without PM. SOM, TC and EDTA-Zn had the most direct influence on soil microbial communities. To improve fertility of soils and maintain quality of soil, rate of application should be 22–44 g PM kg^?1 dm, soil containing Cu and Zn.     

Redistribution of zinc, cadmium, and lead among soil fractions in a sandy calcareous soil due to application of poultry litter

This study was conducted to evaluate, using soil columns, the mobilization and redistribution of heavy metals (Zn, Cd, and Pb) among different soil fractions by soluble organic ligands within poultry litter. Uncontaminated soil was amended with Zn, Cd, and Pb to achieve concentration levels of 400, 8, and 200 mg kg⁻¹ soil, respectively. Columns repacked with this amended soil were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl₂, or poultry litter extract (PLE) solutions. After leaching, the soil samples in the columns were sequentially extracted for exchangeable (EXC), carbonate (CARB) organic matter (OM), Mn oxide (MNO), Fe oxide (FEO), and residual (RES) fractions. Considerable mobilization of Zn, Cd, and Pb occurred in soil during EDTA leaching. Leaching with PLE and CaCl₂ solutions significantly decreased Zn and Cd concentrations in the EXC, CARB, and OM fractions. These solutions significantly decreased Pb concentration in the EXC fraction, while PLE solubilized more Pb from EXC fraction than CaCl₂. Thus, the applied poultry litter may change Zn, Cd, and Pb fractions in metal-amended soil and possibly enhance metal mobility.     

Predicting potentially plant-available lead in contaminated residential sites

Lead (Pb)-based paints pose a serious health problem to people living in residential settings constructed prior to 1978. Children are at a greater risk to Pb exposure resulting from hand-to-mouth activity in Pb-contaminated residential soils. For soil Pb, the most environmentally friendly, potentially cheap, and visually unobtrusive in situ technology is phytoremediation. However, the limiting factor in a successful phytoremediation strategy is the availability of Pb for plant uptake. The purpose of this study was to establish a relationship between soil properties and the plant-available/exchangeable Pb fraction in the selected Pb-based paint-contaminated residential sites. We selected 20 such sites from two different locations (San Antonio, Texas and Baltimore, Maryland) with varying soil properties and total soil Pb concentrations ranging between 256 and 4,182 mg kg^?1. Despite higher Pb levels in these soils that exceeds US EPA permissible limit of 400 mg kg^???1, it is known that the plant-available Pb pools are significantly lower because of their sorption to soil components such as organic matter, Fe?CMn oxides, and clays, and their precipitation in the form of carbonates, hydroxides, and phosphates. Principal component analysis and hierarchical clustering showed that the potentially plant-available Pb fraction is controlled by soil pH in the case of acidic Baltimore soils, while soil organic matter plays a major role in alkaline San Antonio soils. Statistical models developed suggest that Pb is likely to be more available for plant uptake in Baltimore soils and a chelant-assisted phytoextraction strategy will be potentially necessary for San Antonio soils in mobilizing Pb from complexed pool to the plant-available pool. A thorough knowledge of site-specific factors is therefore essential in developing a suitable and successful phytoremediation model.     

Predicting bioavailability of metals from sludge-amended soils

We attempted to develop a protocol for fixing the maximum permissible limit of sludge in agricultural lands based on transfer of metals from sludge-amended soils to human food chain. For this purpose, spinach was grown as a test crop on acid and alkaline soils with graded doses of sludge (0, 1.12, 2.24, 4.48, 8.96, 17.9, 35.8, 71.6, 142 and 285 g kg^?1 of soil) in a pot experiment. Biomass yield of spinach was increased due to sludge application in both acid and alkaline soils. Among the chemical extractants, EDTA extracted the highest amount of metals from sludge-amended soil followed by diethylenetriaminepentaacetic acid (DTPA) and CaCl₂. Elevated levels of Zn, Cu, Fe, Mn, Ni, Cd and Pb in spinach were observed due to sludge application over control. Application of sludge was more effective in increasing metal content in spinach grown on acid soil than alkaline soil. Solubility-free ion activity model as a function of pH, organic carbon and extractable metal was far more effective in predicting metal uptake by spinach grown on sludge-amended soils as compared to that of chemical extractants. Risk in terms of hazard quotient (HQ) for intake of metals through consumption of spinach by humans grown on sludge-treated soils was computed for different metals separately. In a 90-day pot experiment, safe rates of sludge application were worked out as 4.48 and 71.6 g kg^?1 for acid and alkaline soils, respectively.     

Characterization of Organic Compounds in Compost-Amended Soil

Samples of compost-amended soil from waste dumping sites in Lagos Metropolis were extracted with dichloromethane (3 × 20 cm³) and the extract was evaporated at 35 °>C. The residue was extracted with 2,2,4-trimethylpentane, and portions of the solution were applied to a column containing silica gel from which aliphatic and aromatic hydrocarbons were eluted with n-hexane and toluene respectively. Analysis of the n-hexane fraction using gas chromatography showed the presence of a mixture of aliphatic hydrocarbons, ranging from C₉ to C₂₅, while ultraviolet analysis of the toluene fraction suggested 1,2-benzanthracene; 2,3-benzphenanthrene, chrysene and pyrene as polyaromatic compounds present in samples analyzed. The crude extracts were highly coloured and viscous. Total extractable organic residues in the 2,2,4-trimethylpentane extracts ranged from 36 to 89 mg g^-1 of soil.     

Adsorption of ammonium from simulated wastewater by montmorillonite nanoclay and natural vermiculite: experimental study and simulation

In this research, montmorillonite nanoclay (MNC) and vermiculite were used to adsorb ammonium (NH₄ ⁺) from simulated wastewater. The effect of organic acids, cations, and anions on adsorption of NH₄ ⁺ was also studied using batch experiments. The presence of organic acids significantly decreased the NH₄ ⁺ adsorption using both adsorbents and the reduction followed the order of citric acid > malic acid > oxalic acid. The presence of cations in wastewater could decrease the adsorption of NH₄ ⁺ and the ion exchange selectivity on the MNC and vermiculite followed the orders Mg > Ca ≥ K > Na and Mg > > Ca > Na > K, respectively. Adsorption of NH₄ ⁺ by adsorbents in the presence of sulfate (SO₄) was higher than those in the presence of phosphate (PO₄) and chloride (Cl) anions. Results indicated that MNC and vermiculite had good potential for NH₄ ⁺ removal depending on adsorbent dosage, pH, contact time, and initial NH₄ ⁺ concentration. The effect of pH on removal of NH₄ ⁺ indicated that MNC would be more appropriate as the adsorbent than vermiculite at low pH values. Kinetic analysis demonstrated that the rate-controlling step adsorption for NH₄ ⁺ by MNC and vermiculite was heterogeneous chemisorption and followed the pseudo-second-order model. The desorption experiments indicated that the adsorption of NH₄ ⁺ by adsorbents was not fully reversible, and the total recovery of adsorbed NH₄ ⁺ for MNC and vermiculite varied in the range of 72 to 94.6% and 11.5 to 45.7%, respectively. Cation exchange model (CEM) in PHREEQC program was used to simulate NH₄ ⁺ adsorption. Agreement between measured and simulated data suggested that CEM was favored in simulating adsorption of NH₄ ⁺ by clay minerals. The results indicated that MNC and vermiculite have good performance as economic and nature-friendly adsorbents that can ameliorate the water and environment quality.     

Three-dimensional data interpolation for environmental purpose: lead in contaminated soils in southern Brazil

Monitoring of heavy metal contamination plume in soils can be helpful in establishing strategies to minimize its hazardous impacts to the environment. The objective of this study was to apply a new approach of visualization, based on tridimensional (3D) images, of pseudo-total (extracted with concentrated acids) and exchangeable (extracted with 0.5 mol L^?1 Ca(NO₃)₂) lead (Pb) concentrations in soils of a mining and metallurgy area to determine the spatial distribution of this pollutant and to estimate the most contaminated soil volumes. Tridimensional images were obtained after interpolation of Pb concentrations of 171 soil samples (57 points × 3 depths) with regularized spline with tension in a 3D function version. The tridimensional visualization showed great potential of use in environmental studies and allowed to determine the spatial 3D distribution of Pb contamination plume in the area and to establish relationships with soil characteristics, landscape, and pollution sources. The most contaminated soil volumes (10,001 to 52,000 mg Pb kg^?1) occurred near the metallurgy factory. The main contamination sources were attributed to atmospheric emissions of particulate Pb through chimneys. The large soil volume estimated to be removed to industrial landfills or co-processing evidenced the difficulties related to this practice as a remediation strategy.     

Prediction of PAH biodegradation in field contaminated soils using a cyclodextrin extraction technique

Biodegradation has been identified as a major loss process for organic contaminants in soils and, as a result, microbial strategies have been developed for the remediation of contaminated land. Prediction of the biodegradable fraction would be important for determining bioremediation end-points in the clean-up of contaminated land. The aim of this study was to investigate the ability of a cyclodextrin extraction to predict the extent to which polycyclic aromatic hydrocarbons (PAHs) would be degraded microbiologically in field contaminated soils; further testing the robustness and reproducibility of this extraction in chemically complex systems. Dichloromethane and hydroxypropyl-beta-cyclodextrin (HPCD) extractable fractions were measured together with the PAH biodegradable fraction in each of the six field contaminated soils. The amounts of PAHs degraded by the catabolic activity of the indigenous microflora in each of the soils were correlated with HPCD-extractable PAH concentrations. The regressions showed that the amounts of lower molecular weight PAHs extracted by the HPCD were not significantly (P > 0.05) different to the amounts that were degraded. However, higher molecular weight PAHs that were extracted by HPCD did differ significantly (P < 0.05) from the amounts degraded. Although the HPCD extraction did overestimate the microbially degradable fraction of the higher molecular weight PAHs, overall the correlations between the HPCD extractable fraction and the microbially degradable fraction were very close, with mean values of the slope of line for the six soils equalling 1. This study further describes the robust and reproducible nature of the aqueous-based soil extraction technique reliably measuring the extent to which PAHs will be microbially degraded in soil.     

Bioremediation of metal contamination

A study was initiated to evaluate the use of the fungus Aspergillus niger for bioleaching and then todetermine the effect of process steps, the tailingsconcentration and type of substrate. An oxidized miningtailing containing mainly copper (7240 mg kg^-1 tailings) was studied. A sucrose and mineral salts medium was initially used to produce citric and gluconic acids by A. niger atvarious concentrations of tailings (1, 5, 7, 10 and 15% w/v).Maximal removal of up to 60% of the copper was obtained forthe 5% tailings when the organic acid supernatant was addedto the tailings. In a single step process, A. niger wasthen grown in the presence of mining tailings at variousconcentrations. Maximum copper solubilization (63%) occurredwith 10% mining tailings using sucrose as the substrate.Other substrates were then evaluated including molasses, corncobs and brewery waste (10% mining tailings). Sucrose gavethe best results for copper removal, followed by molasses,corn cobs and brewery waste. Other experiments usingultrasound as a pretreatment showed that 80% removal of thecopper could be obtained for a 5% tailings concentration. Inconclusion, leaching of copper from mining tailings istechnically feasible using A. niger but furtherresearch will be required to increase the economic feasibilityof the process.     

PM2.5中重金属形态分布及其在模拟酸雨中的释放

对西安市夏季PM_2.5中6种重金属元素的化学形态进行分析,并研究了模拟酸雨淋溶条件下PM_2.5中6种元素的释放过程。结果表明,近80%的Cr和Fe分布在有机质、氧化物、硫化物结合态和残渣态中,Cd在大气环境中的化学性质很活泼,具有很强的毒害性,Pb、As、和Hg 3种元素主要以碳酸盐态、可氧化态与可还原态存在于环境中;PM_2.5中6种元素均有不同程度的释放,Cd释放率高于其他元素,Fe释放率最低,pH降低有利于颗粒物中重金属元素的释放。     

Soil phosphorus forms and their variations in selected paddy soils of Iran

Fractionation of soil phosphorus (P) can provide useful information for assessing the risk of soil P as the potential sources of eutrophication in aquatic systems. Little information exists on P forms in paddy soils of Isfahan Province in central Iran, where P fertilizers have been continuously applied for at least 45 years. The objectives of this study were to investigate concentrations and proportions of P forms in paddy soils and correlate the content of P forms with basic soil properties. Soil samples from three paddy sites were obtained, and soil P forms were determined by a modified Hedley fraction method. Results show that the total P concentrations ranged from 288 to 850 mg kg^?1 and were enriched in site 1. In all sites, the rank order of P fractions was HCl-P (CARB-P)?>?residual-P (RES-P)?>?NaOH-P (Fe-Al-P)?>?KCl-P (EXCH-P), indicating that Ca compounds are the main soil components contributing to P retention in these calcareous paddy soils. The EXCH-P represented on average?<?1 % of the total P, while the Fe-Al-P ranged 3.3–18 %. The CARB-P showed considerable contribution (63.6–85.6 %) to the total P. The Pearson correlation matrix indicated that Fe-Al-P only was positively correlated with total P, but did not show any significant correlations with other soil geochemical properties. Calcium-bound P fraction was significantly correlated with the clay, silt, cation exchange capacity, and total P.     

Baseline Concentrations of Trace Elements in Surface Soils of the Torrelles and Sant Climent Municipal Districts (Catalonia,Spain)

An investigation was conducted to study the baseline levels of Ba, Cd, Cu, Cr, Ni, Pb, Sr, V and Zn (aqua regia-extractable) based on 51 representative soils of the Torrelles and Sant Climent Municipal Districts (Catalonia, Spain). The baseline concentrations of those elements were (mg kg⁻¹): Ba 73.9–617.9, Cr 9.2–120.2, Cu 4.0–111.6, Ni 6.1–118.6, Pb 5.6–217.5, Sr 19.6–128.8, V 12.1–101.2, and Zn 16.8–326.8, respectively.Forty-nine samples were reported as having less than the 0.67 mg kg⁻¹ detection limit for cadmiun and were therefore not useful for baseline determination; however, these results suggest that the baseline average is probably below 0.67 mg kg⁻¹.Upper baseline values for most of the elements corresponded with those reported in the literature, except for Pb and Zn, which were two to four times greater.Soil properties, including clay fraction, OC, CEC and pH_w were related to metal concentration using correlation and factorial analysis. R-mode factor analysis separates the soil analysis data into three factors. These factors explain 67.3% of the total variance, suggesting that metal concentration was controlled by soil composition.     

Determination of trace transition metals in environmental matrices by chelation ion chromatography

Trace transition metals (Fe^3?+?, Mn, Cu, Cd, Co, Zn, Ni) in environmental samples were analyzed by chelation ion chromatography using a mixed bed ion-exchange column with pyridine-2,6-dicarboxylic acid (PDCA) and oxalic acid as eluent and large volume direct injection (1,000 ??l). The two eluents, PDCA and oxalic acid, were tested, and repeatability and detection limits were compared. The total analysis time was ~15 min. The separation with PDCA was more successful than that obtained with acid oxalic. It was observed that utilizing PDCA resulted in lower detection limits, higher repeatability, and a quantitative detection of Cd and Mn, which coelute as a single peak when using the oxalic acid. At last, the PDCA calibration graphs resulted linear (r ²?>?0.999) in the range 0.4?C1,000 ??g/L. The procedure was applied to the analysis of metals in soils and in water samples. The results obtained from the analysis of natural waters have demonstrated that the method is simple and efficient, therefore, can be used for the determination of metals in natural waters using a continuous and automatic monitoring system.